President Barack Obama and Vice President Joe Biden, along with members of the national security team, receive an update on the mission against Osama bin Laden in the Situation Room of the White House, in this May 1, 2011 handout photo.

The first indication for President Obama that Osama bin Laden had been killed came when a Navy SEAL sent back the coded message to Washington that said simply, "Geronimo-E KIA."

Geronimo was the code name for the operation that sent two teams of 12 SEALS zooming by Blackhawk helicopters to a walled compound in Abbotabad, Pakistan, on Sunday to kill or capture the most wanted man in the world. Anxious White House officials weren't positive that they would find bin Laden in the fortress-like complex, that he might leave while the SEALS were en route.

The first encouraging word came at the beginning of the raid when the SEALS recognized the man who had eluded a U.S. manhunt for a decade. They sent back the message, "Geronimo."

After a 40-minute search of the compound, punctuated by firefights, bin Laden was dead, and the cryptic "Geronimo-E KIA" code sent relief through the White House. E stood for enemy and KIA for killed in action.

Bin Laden was shot twice, once in the head and once in the chest, a senior administration official told ABC News.

The SEALS words, however, were not sufficient proof that the mastermind of the 9/11 terror attacks was finally dead. As the evidence piled up -- verbal ID, face recognition analysis and DNA matches -- the White House debate continued. Obama ended the discussion with a terse, "We got him."

White House senior officials were still sorting through the details today of the dramatic U.S. raid on bin Laden in Pakistan.

Counterterrorism chief John Brennan told reporters that while bin Laden had vowed to go down fighting, in his last moments alive the master terrorist hid behind a woman.

The woman who bin Laden tried to use as a human shield was killed in the U.S. raid, Brennan said. Whether she shielded him willingly is not known.

Brennan said the woman was one of bin Laden's wives, but defense officials said it wasn't clear whether the woman was a bin Laden wife.

The force that swooped down on the world's most wanted terrorist has been identified as SEAL Team Six of the "Naval Special Warfare Development Group."

Brennan, a senior advisor on homeland security, said they were trying to "accomplish the mission safely and securely" for those involved and were not going to give bin Laden a chance to fire back on U.S. forces.

"He was engaged, and he was killed in the process," Brennan said. "If we had the opportunity to take him alive we would have done that."

Brennan called this operation a "defining moment" in war against terrorist groups where they "decapitated the head of the snake."

The three to four hours Sunday night when operation was ongoing, Brennan described as "one of the most anxiety-filled times" and that "minutes passed like days."

Administration officials are now trying to decide whether to release photos of bin Laden's corpse. Releasing the photos would prove that the terror leader is dead, but some officials fear the gruesome nature of the pictures could fan anti-American sentiment.

President Obama Praised Anonymous Heroes Who Killed Bin Laden

Earlier today, Obama praised the anonymous heroes who tracked and killed bin Laden, saying, "we are fortunate to have Americans who dedicate their lives" to defending our country.

"We may not always know their names, we may not always know their stories, but they are always there on the front lines of freedom and we are truly blessed," Obama said in a White House ceremony to honor Medal of Honor winners.

"As commander-in-chief, I could not be prouder of our men and women in uniform," the president said. "That is true now in today's wars, and it has been true in all of our wars and it is why we are here today."

Obama briefly but proudly addressed the top secret raid that killed bin Laden. "I think we can all agree this is a good day for America," he said. "Today we are reminded that as a nation there is nothing we can't do."

He gave special recognition in his speech to Secretary of Defense Robert Gates, calling him "one of the finest secretaries of defense in our history."

When the gunfire stopped, the SEALS quickly moved to determine his identity. Two of the women at the compound identified him and the military flew bin Laden's body to Jalalabad, Afghanistanto have his DNA tested for positive identification. SEALS measured the corpse and determined it to be over 6- feet-4. They then transmitted photographs back to CIA headquarters and agency analysts conducted facial recognition analysis. Their report concluded it was a 90 to 95 percent match.

Bin Laden's DNA was matched with at least two of his relatives, including one of his sisters who died in Boston and whose brain was kept by the United States. The result came back as a 99.9 percent match.

Bin Laden's body was then flown to the aircraft carrier USS Carl Vinson, officials told ABC News and he was buried at sea. The burial was done in accordance with Islamic law, officials said, although there has since been despute over that. A Muslim seaman conducted the process and said the prayers, with bin Laden's body wrapped in the "appropriate way" with a white sheet.

Obama administration officials said it was important to handle the body in accordance with Islamic practices so not to inflame the Muslim world.

Celebrations erupted over night in the United States after the president's televised announcement that "justice has been done." But by this morning the triumphant mood was tinged with caution as security forces braced for possible revenge attacks.

The United States first received a tip in August that the mastermind of the 9/11 terror attacks was hiding in a million-dollar mansion with 12 to 15 foot walls.

The evidence that bin Laden was hiding there was largely circumstantial and he had not been seen, sources told ABC News, and officials did not know where he may be in the sprawling compound that is located about 1,000 feet away from the Pakistan Military Academy.